As a sealing material composition which is used for producing a sealing material, for example, known is a yarn which is disclosed in Patent Literature 1. A yarn of this kind is configured by a tubular member which is formed by knitting or braiding a fibrous material, and a plurality of fibrous members (fibrous expanded graphites) which are filled into the tubular member.
Each of the plurality of fibrous expanded graphites is a flexible long member. The fibrous expanded graphites are charged into the tubular member so that their longitudinal directions approximately coincide with the longitudinal direction of the tubular member, and then filled into the tubular member while being flexurally deformed, in a state where the fibrous expanded graphites are randomly arranged (see FIG. 6).
In the tubular member, therefore, uneven gaps are easily formed between adjacent ones of the plurality of fibrous expanded graphites. In a usual sealing material composition, consequently, such gaps are contained in a large number. Moreover, these gaps tend to exist at relatively short intervals in the longitudinal direction of the tubular member.
In the case where, for example, a sealing material is to be produced by using the yarn, or the yarn is to be conveyed while being wound around a round rod-like member such as a bobbin, when the yarn is flexed and curved, therefore, there is a case where the yarn is sharply bent in the curved portion, and one(s) of the plurality of fibrous expanded graphites is broken.
In such a yarn, when a bending action is applied by an external force, namely, a predetermined amount of flexure is allowed in accordance with the external force, but, when an external force greater than a permissible amount is applied, breakage may possibly occur in the plurality of fibrous expanded graphites. Therefore, there is a possibility that breakage in the plurality of fibrous expanded graphites may cause the performance of a sealing material which is produced by using the yarn, to be lowered.
Conventionally, a fluid apparatus such as a pump or a valve is provided with a gland packing as the above-described sealing material. A gland packing of this kind is configured by using an inner core member, and a plurality of yarns which are bundled around the inner core member in a state where the yarns are twisted or braided together (for example, see Patent Literature 2).
When the gland packing is to be used, the gland packing is firstly adjusted so as to have a predetermined longitudinal length. While maintaining the state, then, the gland packing is formed into a ring-like shape or compress-molded into a ring-like shape according to the shaft member of a predetermined fluid apparatus. Thereafter, the gland packing is stuffed and disposed into a stuffing box which is located in the periphery of the shaft member in the fluid apparatus.
In the gland packing, the inner core member is configured by the tubular member formed by knitting or braiding fibrous materials, and the plurality of fibrous expanded graphites filled into the tubular member. Therefore, there sometimes occurs a case where, when the gland packing is curved so as to exhibit a ring-like shape, the inner core member is sharply bent in the curved portion, and one(s) of the plurality of fibrous expanded graphites is broken.
In the inner core member, when a bending action is applied by an external force, namely, a predetermined amount of flexure is allowed in accordance with the external force, but, when an external force greater than a permissible amount is applied, breakage may possibly occur in the plurality of fibrous expanded graphites. Therefore, there is a fear that breakage in the plurality of fibrous expanded graphites may cause the sealing property of the inner core member and hence that of the gland packing, to be lowered.